This invention is concerned with improvements in or relating to presses, especially presses comprising two platens one of which is movable relative to the other to effect an operating stroke of the press, and fluid pressure operated means comprising a plurality of piston and cylinder arrangements for effecting movement of the movable platen.
There is described in the specification of the commonly owned copending U.S. patent application Ser. No. 390,250 a press comprising two platens one of which is movable relative to the other to effect an operating stroke of the press, fluid pressure operated means comprising a plurality of piston and cylinder arrangements for effecting movement of the movable platen, a plurality of spool valves, one associated with each of the piston and cylinder arrangements, the spool of each of said valves being engageable by valve actuating means, and actuation of the spool valves being effective to admit fluid under pressure to the piston and cylinder arrangements, and drive means for moving the valve actuating means simultaneously to move the spools of said valves to admit fluid under pressure to the piston and cylinder arrangements and to maintain the spool valves in actuated condition as the movable platen moves to effect an operating stroke of the press.
In the press described in detail in said specification, the spool valves are mounted for movement with the movable platen and the drive means is effective to move the valve actuating means to engage the valve spools, thus to initiate an operating stroke of the press, and thereafter continues to move the valve actuating means to maintain the spool valves in actuated condition. The drive means of said press comprises a plurality of lead screws, driven by a single motor through connecting means having a 1:1 ratio. The valve actuating means comprises two bars extending between the spools and each arranged to engage two spools so as to operate the spools simultaneously. The motor of the drive means is a conventional hydraulic motor which operates through a reduction gear unit in order to control the speed of drive of the valve actuating means.
More specifically, in said press the lower platen is mounted for movement relative to the upper platen to effect an operating stroke of the press, the lower platen being mounted for this purpose on a plurality of, in this case four, cylinders which are movable upon admission of fluid under pressure thereto, on stationary pistons, piston rods of which are secured to the press frame. The spool valves are mounted on their associated cylinders and the spools thereof have a downwardly projecting portion arranged to be engaged by the bars constituting the valve actuating means, each bar being supported at its ends by the lead screws which are synchronously driven.
Although the use of lead screws has been shown to be effective in operation, nevertheless it has been shown to be expensive to produce a system which utilizes a hydraulic motor cooperating with such lead screws. It is one of the various objects of the present invention, therefore, to provide an improved press in which a valve actuating system is provided which is equally effective in operation as the earlier system, but which is less expensive to produce.